Textural and catalytic properties of MCM-22 zeolite crystallized by the vapor-phase transport method

Article abstract of DOI:10.1246/bcsj.77.1249

MCM-22 zeolite crystallized by the vapor-phase transport (VPT) method showed a higher shape-selectivity to p-xylene in the alkylation of toluene with methanol, compared with MCM-22 crystallized by the hydrothermally synthetic (HTS) method, because VPT-MCM-22 has a smaller external surface area and a smaller number of acid sites thereon than HTS-MCM-22. Such textural properties of VPT-MCM-22 are caused by the fact that the spherical particles of VPT-MCM-22 are composed of hexagonal plates as thin as 55 nm; they are larger than those of HTS-MCM-22, which are 30 nm thick. The acidic properties, characterized by NH₃-TPD and FT-IR using a pyridine adsorption technique, showed no significant difference between VPT- and HTS-MCM-22, except for the acidity on the external surface.

Full text of DOI:10.1246/bcsj.77.1249

ꢀ 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 1249–1254 (2004) 1249
Textural and Catalytic Properties of MCM-22 Zeolite Crystallized
by the Vapor-Phase Transport Method
ꢀ
Satoshi Inagaki, Kohei Kamino, Masahiro Hoshino, Eiichi Kikuchi, and Masahiko Matsukata
Department of Applied Chemistry, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555
Received November 17, 2003; E-mail: sinagaki dr@ruri.waseda.jp
MCM-22 zeolite crystallized by the vapor-phase transport (VPT) method showed a higher shape-selectivity to p-xy-
lene in the alkylation of toluene with methanol, compared with MCM-22 crystallized by the hydrothermally synthetic
(HTS) method, because VPT-MCM-22 has a smaller external surface area and a smaller number of acid sites thereon than
HTS-MCM-22. Such textural properties of VPT-MCM-22 are caused by the fact that the spherical particles of VPT-
MCM-22 are composed of hexagonal plates as thin as 55 nm; they are larger than those of HTS-MCM-22, which are
30 nm thick. The acidic properties, characterized by NH3-TPD and FT-IR using a pyridine adsorption technique, showed
no significant difference between VPT- and HTS-MCM-22, except for the acidity on the external surface.
Hydrothermally synthesized MCM-22 zeolite using hexahy-
dro-1H-azepine (hexamethyleneimine, HMI) as a structure-di-
recting agent1 is designed as an MWW structure, and has the
same topology as PSH-3,2 SSZ-25,3 ERB-1,4 and ITQ-15
sired phase. These early reports,15,16 as well as the original pat-
ent,1 indicate that stirring or rotating during hydrothermal crys-
tallization is necessary to obtain a high-quality MWW phase.
Crystallization by using HMI under static conditions yielded
a pure phase of MCM-22 for narrow ranges of synthetic param-
eters, such as the gel composition, crystallization period and
temperature.15,17,18
ꢀ
( three letter codes representing the zeolite structures are de-
fined by the International Zeolite Association6). This type of
zeolite has a large pocket (inner diameter of 0.71 nm) on the ex-
ternal surface and two independent pore systems with 10-mem-
bered ring (10MR): one is defined by a two-dimensional sinus-
oidal channel, and the other by the 12MR supercages.7,8 Much
attention has been paid to the unique crystalline structure due to
possibilities of being applied to many catalytic reactions, such
as the selective production of p-xylene in the disproportiona-
tion of toluene9 and the aromatization of n-butane.10 This zeo-
lite has recently enabled commercial processes of ethylbenzene
and cumene production by the alkylation of benzene with eth-
ylene and propylene.11,12
The stirring/rotating crystallization yielded isolated hexago-
nal thin plates (around 1 mm in width) of MCM-22 crystals,
whereas static crystallization gave crystals composed by the ag-
gregation of hexagonal thin plates. Guray et al.18 suggest that
¨
the aggregation of thin plates resulted in a limitation on the
mass transfer of nutrients from the solution to the growing crys-
tals during static crystallization, if compared with the rotating/
stirring conditions.
In our previous research,19 MCM-22 zeolite crystallized by
the vapor-phase transport (VPT) method, which is one of the
dry gel conversion techniques for zeolite synthesis,20–23 con-
sisted of aggregates of hexagonal thin plates, similarly to a
crystal crystallized by the hydrothermally synthetic (HTS)
method under static conditions. In this study, we investigated
the physicochemical and catalytic properties of MCM-22 zeo-
lite crystallized by the VPT method compared with the crystal
obtained by the HTS method.
The morphologies of zeolite catalysts have been demonstrat-
ed to significantly change the catalytic activity and selectivity.
For instance, larger ZSM-5 particles with smaller external sur-
face area showed higher p-xylene selectivity than smaller
ZSM-5 particles in the alkylation of toluene with methanol
and the disproportionation of toluene.13,14 The crystal morphol-
ogies (size, aspect ratio, shapes) of zeolites could be changed
by controlling the hydrothermal conditions of crystallization,
for example, the compositions of the parent hydrogel, aging
temperature and period, crystallization temperature and period
and stirring/rotating speed.
The hydrothermal synthesis of MCM-22 zeolite has been
studied in detail15–18 using HMI. In early reports,15,16 MCM-
22 having SiO2/Al2O3 ratios of around 30 could be obtained
as a pure phase for a relatively board range of OH/SiO2 ratios,
whereas crystallization from a parent mixture with low alumi-
num contents (i.e., SiO2/Al2O3 = 70) yielded a mixture of the
MWW phase with the MFI15 or the FER16 phase. Mochida and
co-workers16 reported that seeding in the hydrothermal synthe-
sis of MCM-22 zeolite could avoid the formation of an unde-
1. Experimental
1.1 Synthesis of an MCM-22 Precursor by the VPT Method.
An MCM-22 precursor having an MWW-type framework was syn-
thesized by the VPT method according to our previous report,19 us-
ing HMI as a structure-directing agent. In a typical procedure, the
hydrogel was prepared by mixing appropriate amounts of fumed
silica (99.8% purity, Aldrich), NaAlO2 (Al2O3: 36.5 wt %, Na2O:
33.0 wt %, Kanto Chem.), NaOH pellet (96.0% purity, Kokusan
Chem.) and distilled water. The composition of the mixture was
SiO2:Na2O:Al2O3:H2O = 1.0:0.075:0.028:44. The hydrogel was
stirred vigorously for 30 min at room temperature, followed by
ꢁ
drying on a hot stirrer at 80 C overnight. Dry gel weighing 0.5
Published on the web June 9, 2004; DOI 10.1246/bcsj.77.1249

1250 Bull. Chem. Soc. Jpn., 77, No. 6 (2004)
Textural/Catalytic Properties of VPT-MCM-22
The amount of Al in MCM-22 zeolites was measured by
using inductively coupled plasma spectrometry (ICP, CIROS-120,
Rigaku).
The number of acid sites was measured by using the tempera-
ture-programmed desorption (TPD) of ammonia. The catalyst em-
ployed was evacuated at 500 ꢁC prior to the measurement. The
TPD data were collected at a ramping rate of 1 ꢁC minꢂ1. A mass
spectrometer was used to monitor the desorbed ammonia. The
number of acid sites was determined from that of the desorbed
ammonia.
Fig. 1. Setup of autoclave for the vapor-phase transport
(VPT) method.
Bronsted and Lewis acid sites on MCM-22 zeolite were charac-
¨
terized by pyridine adsorption with Fourier transform infrared
spectrometry (FT-IR). Self-supporting pressed wafers (diameter,
2 cm; weight, 20 mg) were prepared and activated by heating under
a dynamic vacuum for 1 h at 500 ꢁC, in an IR cell allowing in situ
thermal treatments and low-temperature gas dosage. After cooling
g was crushed to a powder and placed in a 50 mL autoclave. The
autoclave was set up so as to separate the dry gel from a liquid mix-
ture of HMI (>97:0% purity, Kanto Chem.) and distilled water, as
shown in Fig. 1. In this study, 1.5 g of HMI and 2.0 g of distilled
water were added to the bottom of the autoclave. The dry gel was
ꢁ
to 150 C, adsorbing pyridine vapor (ca. 2.6 kPa) and evacuating
gases, IR spectra were recorded on the FT-IR (FT-610, JASCO)
ꢁ
crystallized under autogeneous pressure at 150 C for 3–7 days.
The products were filtered, washed with distilled water, and dried
with a resolution of 4 cmꢂ1
.
ꢁ
at 110 C.
1.5 Catalytic Tests. The alkylation of toluene with methanol
was performed under atmospheric pressure in a downflow quartz-
tube microreactor with 8 mm of inner diameter. Prior to running
the reaction, 10 or 20 mg of a catalyst was packed in a fixed-bed
of the reactor with 2.0 g of silicon nitride as a diluent, and preheat-
ed at 350 ꢁC for 1 h in a stream of argon. After reducing the tem-
perature to 250 ꢁC, the feed was switched over to an argon stream
containing an equimolar mixture of toluene and methanol. The ar-
gon stream contained 5% of methane as an internal standard mate-
rial. The reactants and products were separated by using a packing
column with Bentone 34 (5%) + diisodecylphthalate (DIDP) (5%)
(GL Science) and analyzed by using GC-8A (Shimadzu) with a
flame-ionization detector.
1.2 Synthesis of MCM-22 Precursor by HTS Method.
MCM-22 precursor was also synthesized hydrothermally accord-
ing to the following procedure. A mixture of fumed silica, NaAlO2,
NaOH, HMI, and distilled water was prepared and stirred vigorous-
ly for 30 min at room temperature. The mixture was composed of
SiO2:Na2O:Al2O3:H2O:HMI = 1.0:0.075:0.028:44:0.5, and was
ꢁ
transferred into an 100 mL autoclave and crystallized at 150 C
for 5–7 days under rotating conditions. The rotating speed was
20 rpm. The products were filtered, washed with distilled water,
ꢁ
and dried at 110 C.
1.3 Preparation of Hþ-MCM-22 Zeolite. The formation of
MCM-22 zeolite requires the calcination of an as-synthesized
product, defined as an MCM-22 precursor. The precursor was cal-
cined in an air flow at 540 ꢁC for 12 h (ramping rate = 5 ꢁC minꢂ1).
The calcined product, defined as MCM-22 zeolite, was treated by
repeated ion exchange in 1 M NH4NO3 aqueous solution at 80 ꢁC
for 1 h with stirring four times. The NH4þ-MCM-22 zeolites were
calcined again in air at 540 ꢁC for 12 h (ramping rate = 5
ꢁC minꢂ1) in order to degas NH3, and then Hþ-MCM-22 zeolites
were obtained.
The cracking of 1,3,5-triisopropylbenzene (TIPB) at 200 ꢁC was
carried out by a pulse method as a catalytic test to evaluate the
number of acid sites on the external surface of the MCM-22 zeo-
lite. Before the reaction, 10 mg of a catalyst was packed in a
fixed-bed of a stainless-tubeꢁmicroreactor with a 4 mm inner diam-
eter, and preheated at 350 C for 1 h in a stream of helium (30
ꢁ
cm3 minꢂ1). After reducing the temperature to 200 C, 1.0 mL of
TIPB was pulsed into the catalyst-bed with a stream of helium
(30 cm3 minꢂ1). The reactant and the products of cracking were
separated by using a packed column with OV-1 (GL Science),
and detected by using GC-8A (Shimadzu) with a thermal-conduc-
tivity detector.
In this report, the as-synthesized MCM-22 precursor and the cal-
cined MCM-22 zeolite are designated as MCM-22(P) and MCM-
22, respectively. In the cases of crystallization using the VPT
and HTS methods, VPT- and HTS- are prefixed to MCM-22(P)
or MCM-22; for instance, the MCM-22 precursor crystallized by
the VPT method is designated as VPT-MCM-22(P).
1.4 Characterization. All of the as-synthesized and calcined
products were checked concerning their crystallinity and phase pu-
rity by X-ray powder diffraction (XRD) on an RINT 2000 (Rigaku)
equipped monochromator and scintillation counter, using Cu Kꢀ
radiation at 40 kV and 20 mA.
The scanning micrographs for the products were obtained on an
S-4500S field-emission scanning electron microscope (FE-SEM,
Hitachi) at an accelerating voltage of 15 kV. The samples were
sputtered with a mixture of platinum and palladium before taking
the images.
2. Results and Discussion
2.1 Morphologies and Textural Properties of VPT- and
HTS-MCM-22 Zeolites. As confirmed by XRD, shown in
Fig. 2c, VPT-MCM-22(P) was crystallized at 150 ꢁC for 7 days
with the addition of 1.5 g of HMI and 2.0 g of H2O in the liquid
phase in a 50 mL autoclave. A shorter crystallization period of
only 3 days gave an amorphous product (Fig. 2a), and a crystal-
lization period of 5 days was sufficient to crystallize an MWW
structure (Fig. 2b). The crystallization of HTS-MCM-22(P) al-
so required 5 days, as confirmed by XRD (shown in Fig. 2d).
The intensities of the XRD patterns for the products after more
than 5 days of crystallization were hardly changed (Fig. 2e).
Hereafter, the MCM-22 products obtained by crystallization
for 7 days either by the VPT or by the HTS method are charac-
terized.
The textural properties of MCM-22 zeolites were determined
from a N2 sorption experiment at ꢂ196 ꢁC on AUTOSORB-1
ꢁ
(Quantachrome Inst.). The sample was evacuated at 350 C for 3
h prior to a measurement. The external surface area and the micro-
pore volume were determined from the adsorption branch by using
the t-plot method.24

S. Inagaki et al.
Bull. Chem. Soc. Jpn., 77, No. 6 (2004) 1251
The XRD pattern for VPT-MCM-22 gave shaper peaks than
that of HTS-MCM-22, if compared to Figs. 3a and 3b, suggest-
ing that VPT-MCM-22 consisted of larger crystallites than
HTS-MCM-22. The crystallinity of HTS-MCM-22, however,
was comparable to that of VPT-MCM-22, if we considered
no appreciable difference in the micropore volume between
VPT- and HTS-MCM-22, as shown in Table 1 to be 0.150
cm3 gꢂ1 and 0.144 cm3 gꢂ1. The micropore volume and the ex-
ternal surface area were determined by using t-plot curves, as
shown in Fig. 4. In contrast, the external surface area of
HTS-MCM-22 (262 m2 gꢂ1) was much larger than that of
VPT-MCM-22 (150 m2 gꢂ1), caused by a difference in the
thickness of the thin plates composing MCM-22 crystals, as
demonstrated by the FE-SEM images given in Fig. 5. VPT-
MCM-22 had the shape of a sphere with a diameter of around
15 mm (Fig. 5a); these spherical particles were actually the ag-
gregate of thin plates with about 45–65 nm thickness (Fig. 5b).
On the other hand, HTS-MCM-22 had a hexagonal shape,
which was composed of isolated thin plates with a 25–35 nm
thickness isolated and about 1 mm length (Figs. 5c and 5d).
2.2 Catalytic Properties of VPT- and HTS-MCM-22.
The number of Bronsted acid sites on the external surface,
¨
which depends on the external surface area, was considerably
different between the VPT- and HTS-MCM-22 zeolites. This
difference was confirmed by comparing the activity for TIPB
cracking. The proton-type HTS-MCM-22 showed a 74% con-
ꢁ
version of TIPB at 200 C, higher than that of VPT-MCM-22
(41%), as shown in Table 1. Only the number of acid sites on
the external surface was different between these two MCM-
22 catalysts. There were no significant difference in the acidic
properties, which have so far been characterized by NH3-TPD
and FT-IR using the pyridine adsorption technique. These
MCM-22 zeolites had almost the same amount of whole acid
sites, which was proved by NH3-TPD, as shown in Fig. 6 and
Table 1. In both MCM-22 zeolites, the acid sites measured
by NH3-TPD originated from Al species included in MCM-
22 powder, because the amount of Al in MCM-22 was equal
to that of the acid sites, as listed in Table 1. The relative number
of Bronsted to Lewis acid sites on VPT-MCM-22 was almost
¨
the same as that on HTS-MCM-22, since the relative intensities
of two peaks at 1540 and 1450 cmꢂ1, respectively, correspond-
ing to pyridine adsorbed on Bronsted and Lewis acid sites, were
¨
not significantly different between VPT- and HTS-MCM-22
Fig. 2. ꢁ XRD patterns for as-made products crystallized at
150 C by the VPT method for a) 3 days, b) 5 days, c) 7
days and by the HTS method for d) 5 days, e) 7 days.
Fig. 3. XRD patterns for calcined MCM-22 zeolites crystal-
lized at 150 ꢁC for 7 days by the VPT (a) and HTS (b)
methods.
Table 1. Textural, Acidic, and Catalytic Properties of MCM-22 Zeolites
Micropore
volume
/cm3 gꢂ1
External
surface area
/m2 gꢂ1
Average of thickness
of thin plate
/nm
Number of
acid sitebÞ
/mmol gꢂ1
Number of Al
in MCM-22cÞ
/mmol gꢂ1
% Conversion
of TIPBaÞ
Catalyst
VPT-MCM-22
HTS-MCM-22
0.150
0.144
150
262
55 ꢃ 10
30 ꢃ 5
41
74
0.97
1.13
1.09
1.02
a) Reaction conditions for cracking of 1,3,5-triisopropylbenzene (TIPB): temperature, 200 ꢁC; weight of catalyst, 10 mg;
He flow rate, 30 cm3 minꢂ1; pulse width of TIPB, 1.0 mL. b) The amount of acid sites was determined by NH3-TPD. c)
The amount of Al in MCM-22 was determined by ICP.

1252 Bull. Chem. Soc. Jpn., 77, No. 6 (2004)
Textural/Catalytic Properties of VPT-MCM-22
Fig. 4. t-Plot curves calculated from nitrogen adsorption isotherm for a) VPT-MCM-22 and b) HTS-MCM-22 zeolites.
ꢁ
Fig. 5. FE-SEM images for calcined MCM-22 zeolites crystallized at 150 C for 7 days by the VPT (a, b) and HTS (c, d) methods.
zeolites, as demonstrated by the FT-IR spectra (Fig. 7).
sites.
On either MCM-22 catalyst, dimethyl ether (DME) was
formed by the intermolecular dehydration of methanol, which
was faster than the alkylation of toluene with methanol, as
shown in Table 2. The yield of DME was determined by the
following Eq. 1:
As shown in Table 2, the MCM-22 catalyst showed a high
selectivity toꢁp-xylene in the alkylation of toluene with meth-
anol at 250 C, as attributed to shape-selective alkylation in
10MR micropore of the MWW structure, similarly to ZSM-
5.13 Moreover, the p-xylene selectivity of VPT-MCM-22 was
always higher than that of HTS-MCM-22, over the whole range
of W/F studied, due to a smaller number of acid sites on the ex-
ternal surface of VPT-MCM-22. The smaller fraction of the ex-
ternal surface acidity on the VPT-MCM-22 gave lower levels
of conversion, based on either toluene or methanol, than did
HTS-MCM-22, in spite of almost the same total number of acid
Yield of DME (%)
(Amount of DME formed) ꢄ 2
Amount of methanol in a mixture of reactants
¼
ꢄ 100:
ð1Þ

S. Inagaki et al.
Bull. Chem. Soc. Jpn., 77, No. 6 (2004) 1253
Fig. 6. NH3-TPD spectra for a) VPT-MCM-22 and b) HTS-
MCM-22 zeolites.
Fig. 7. FT-IR spectra of adsorbed pyridine on the VPT (a)
and HTS (b) MCM-22 zeolites.
Table 2. Product Distributions in the Alkylation of Toluene with Methanol over MCM-22 Zeolites
Product distribution in alkylated products/%
(W/F)/g h
(mol-methanol)ꢂ1
% Conversion % Conversion Yield of
Catalyst
1,3,5-
TMB
1,2,4-
TMB
1,2,3-
TMB
of toluene
of methanol DME/% p-X
m-X
o-X
VPT-MCM-22
0.66
1.37
2.02
1.4
2.9
3.9
30.0
40.9
59.3
28.5
38.4
55.0
63.6
57.4
55.3
12.7
14.2
14.5
20.9
20.7
20.7
0.0
0.0
0.0
2.8
6.5
8.2
0.0
1.2
1.2
HTS-MCM-22
0.69
1.35
2.08
1.8
3.1
5.4
ꢁ
36.9
49.9
65.8
34.9
46.5
59.8
44.0
41.8
40.4
14.7
14.3
15.2
37.9
36.1
32.5
0.0
0.0
0.0
3.4
5.1
8.9
0.0
2.6
3.1
Reaction conditions: temperature, 250 C; weight of catalyst, 10 or 20 mg; partial pressure of methanol, 9 kPa; partial pressure of
toluene, 9 kPa; time on stream, 5 min. DME, dimethyl ether; X, xylene; TMB, trimethylbenzene.
As shown in Fig. 8, there was no appreciable difference in the
selectivity to DME on the basis of methanol between VPT- and
HTS-MCM-22, since there was no significant difference in the
acidic properties, as confirmed by NH3-TPD and FT-IR.
3. Conclusions
The main results from our studies can be summarized as
follows:
(a) VPT-MCM-22 zeolite has the shape of a sphere composed
of hexagonal plates as thin as 55 nm, which are larger than
those of HTS-MCM-22 (30 nm thick).
(b) Thus, VPT-MCM-22 has a smaller external surface area,
and the number of acid sites thereon compared with HTS-
MCM-22.
(c) In the alkylation of toluene with methanol at 250 ꢁC, the p-
xylene selectivity of VPT-MCM-22 catalyst was always higher
than that of HTS-MCM-22, due to a smaller number of acid
sites on the external surface of VPT-MCM-22.
(d) In contrast, the acidic properties characterized by NH3-TPD
and FT-IR using the pyridine adsorption technique showed no
significant difference between VPT- and HTS-MCM-22,
except for the acidity on the external surface.
Fig. 8. Conversion of toluene ( , ) and yield of DME (
,
) against conversion of methanol in alkylation of toluene
with methanol on MCM-22 zeolites. Blank mark means
VPT-MCM-22; filled mark means HTS-MCM-22.

1254 Bull. Chem. Soc. Jpn., 77, No. 6 (2004)
Textural/Catalytic Properties of VPT-MCM-22
248,’’ ed by T. E. Whyte, Jr., R. A. Dalla Betta, E. G. Derouane,
and R. T. K. Baker, American Chemical Society, Washington,
D.C. (1984), Chap. 14.
14 J.-H. Kim, T. Kunieda, and M. Niwa, J. Catal., 173, 433
(1998).
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